Currently, on a long term evolution (LTE) system, an adaptive modulation and coding of a physical downlink shared channel (PDSCH) follows the procedure: a terminal device estimates channel information that is used for measuring channel state information (CSI); the terminal device calculates a signal to interference plus noise ratio (SINR) by using the channel information and based on an optimal rank indication (RI) and/or an optimal precoding matrix indication (PMI); the terminal device obtains a corresponding channel quality indicator (CQI) according to the SINR and reports a value of the CQI to a base station; and the base station allocates a modulation and coding scheme (MCS) to the terminal device according to the channel quality indicator (CQI) CQI value reported by the terminal device and a network situation, where the MCS is used for indicating a modulation scheme and a coding scheme that are currently used on the PDSCH.
In a hotspot scenario, for example, in a scenario of relay (Relay) or LTE hotspot improvements (LTE-Hi), a terminal device needs a modulation scheme higher than 64 quadrature amplitude modulation (QAM); however, due to a limitation in the prior art, a greatest CQI value is 15 and a modulation scheme corresponding to the greatest CQI value is 64QAM, which means that the terminal device is unable to select a modulation scheme higher than 64QAM, and system performance is adversely affected. Similarly, the base station is unable to allocate a modulation scheme higher than 64QAM to the terminal device, either.